U.K. fashion giant Asos has confirmed a data breach involving customer personal information, after hackers used the company’s own app to notify users of a hack.

The breach involves names, contact information, home addresses, phone numbers and email addresses, as well as notes on customer profiles, including website search queries.

The hackers reportedly impersonated a trusted contact to obtain login credentials, breaking into a Snowflake instance, a tech platform used by Asos to analyze large amounts of data. They then used the company’s own notification system to alert customers, pressuring the company into engaging with them or risk having their data published online.

Asos has 17 million customers, and the hack comes as a reminder of the complexity in securing digital systems. Earlier this year, fintech giant Betterment faced a similar breach.

The incident highlights the need for increased security measures and the potential vulnerabilities in third-party platforms and in-house systems.